Internal combustion engines may use lubricating oil for many purposes including, for example, lubricating moving parts, actuating cam phasers, and controlling valve lifters for valve stepping and cylinder deactivation. Cam phasers and cylinder deactivation devices generally require a higher oil pressure for actuation during engine operation than the moving parts of the engine require for proper lubrication.
One approach to maximize engine efficiency is to use a smaller oil pump to provide only the minimum amount of oil pressure needed to prevent engine wear. However, smaller oil pumps do not provide enough oil pressure to actuate a cam phaser or switching lifters at low and idle engine speeds. Thus, cam phasing, valve stepping, and cylinder deactivation can only be achieved at higher engine speeds.
Another approach is to use a larger oil pump to provide enough oil pressure to operate the cam phaser or switching lifters at low engine speeds. This approach allows phasing, valve stepping, and cylinder deactivation at lower engine speeds to alter the valve timing and increase engine efficiency. However, the efficiency gains are not without cost. A higher pressure produced by larger oil pump supplies excess flow that over lubricates the moving parts of the engine and requires additional energy to drive the pump, creating parasitic losses that reduce engine efficiency.
A method is desired of selectively regulating oil pressure throughout an engine to increase engine efficiency while allowing the engine to operate a cam phaser or switching lifters at low engine speeds without having to greatly increase oil pump output.